Telecommunication satellites usually comprise a platform and a payload, the latter being comprising all equipments, notably all devices intended for generating and transmitting high power radiofrequency signals—hereinafter referred to as RF signals—toward the ground. Different known techniques are resorted to for transmitting high power RF signals.
A first technique is based on the solid state technology, and involves Solid State Power Amplifiers, usually referred to as SSPAs. SSPAs notably have the drawback of not being in a position to manage usually requested levels of RF power.
A second technique is based on the use of Travelling Wave Tube Amplifiers, hereinafter referred to as TWTAs. TWTAs notably comprise a Travelling Wave Tube, hereinafter referred to as TWT. Telecommunication satellite payloads nowadays extensively use TWTAs. TWTAs are particularly efficient devices for high power RF transmission channels, and allow for managing very high levels of transmitted RF power. However, TWTA relies on a tube-based technology which requests a very precise tuning, not only on the manufacturing level, but also as regard to the accuracy of electrical interfaces. A TWT is described in much detail below in reference to FIG. 1, and basically comprises an RF input and an RF output, a helix, and electrodes comprising a cathode emitting electrons forming an electron beam, an anode, usually referred to as “Anode Zero” or “Anode 0”, focussing the electron beam, and a plurality of collectors.
Moreover, each produced TWTA is unique, and optimized for the purpose of a unique application, in terms of transmitted frequency, level of transmitted power and efficiency. Once designed, manufactured and possibly optimized, a TWTA and its associated control equipment have to keep operating the same way all through a satellite's assembly, integration and testing, and the in-flight mission of the satellite they are set in. That is: once the telecommunication satellite has been assembled, these equipments shall be operated under the specific conditions they have been designed for. Besides, the efficiency performance of TWTAs is frequency-dependent. Therefore, in parallel, a satellite intended for transmitting through a plurality of channels, shall be containing as many TWTAs, with related consequences in terms of cost, weight and bulk. Also, one TWTA being usually destined to transmit through one given channel over a typical mission duration of more than 15 years makes the payload design and the TWTA procurement very constraining and induces severe constraints in terms of risk management.
Wide-band TWTAs are known in the prior art, but existing devices typically suffer an efficiency degradation of about 2 percents compared to analogue TWTAs optimized in a narrower RF band.
For all above-mentioned reasons, a very long and costly part of a telecommunication satellite payload development is to propose a technical answer to the final customer needs, in terms of number of channels, frequency and power allocation, minimizing the power demand to the platform and within given reliability requirements.